These
limits are governed by
the relationship of
what is inside the
cell to the area of
the membrane that
encloses the cell.

The
incredible giant cell
would have so much
chemistry going on
inside itself that it
could not get food,
minerals, and water to
come in through the
cell wall fast enough
to keep it alive.

However,
tiny cells that cause
us to get the flu have
enough area on the
outside to keep the
chemistry inside
working very
well!

Let's
think about this for a minute. The cell is
a little parcel of just the right chemicals. To live, it must
keep its chemical contents balanced.

This is accomplished by

letting necessary chemicals into the cell
-- such as oxygen,
water, and
minerals

letting waste products get out through the
cell membrane.

A process called
diffusion
allows chemicals
to pass through the cell membrane. The cell has no
mouth, no lungs, no digestive system. Everything has to happen
through the membrane. The relationship between the
surface area of the
membrane and the volume of the contents of the cell becomes the
limiting factor in cell size.

Here is something interesting. Look at how
the area (size of the
surface) of the outside changes with the shape even though the
volume (inside) stays the same.

Compute
the Area

Total
Surface Area
(the outside)

Volume
(the inside)

2 inches by 2 inches
by 2 inches

( 2 * 2) * 6 sides =

24
square
inches

Area = 24
square inches

2 * 2 * 2 =

8
cubic inches

1 inch by 1 inch by
8 inches

(1 * 1) *2 sides =
2
plus
( 1 * 8) * 4 sides = 32

( 2 + 32 ) = 34 square
inches

Area = 34
square inches

1 * 1 * 8 =

8
cubic
inches

2 inches
by 1 inch
by 4 inches

( 2 * 1 ) * 2 sides =
4plus

(4 * 1 ) * 2 sides =
8
plus

(4 * 2) * 2 sides =
16

(
4 + 8 + 16 ) =
28

Area = 28
square
inches

2 * 1 * 4 =

8 cubic inches

When a cell gets too big it will starve from
lack of incoming chemicals, or poison itself with wastes that
cannot be excreted rapidly enough, so it will try to maximize
the surface area to volume ratio. (This works in water. On land
increased surface area also means faster dehydration and heat
loss (or gain).

However -- the cell becomes more fragile as
it elongates and thins itself. This creates practical limits
to how large the cell can grow.

A strategy that increases the area of the
cell surface and also strengthens it is to grow little pleats
and ridges. Here are some examples of cells that have done this.